Referring to FIG. 1, in a sound space, a head-related transfer function (HRTF) represents change from an original sound from a sound source S to listening sound at a listener U. The position of the sound source S is represented by a radius vector r and angles A and B in polar coordinates of which the position of the listener is the origin O. The radius vector r is a distance from a middle point of the listener's head to the position of the sound source S; the angle A is an azimuth angle formed by a front or rear direction of the listener and a direction of the sound source S in a horizontal plane. The angle B is an elevation angle formed by a horizontal plane including the position of the listener and the direction of the sound source S in a vertical plane.
Conventional methods of measuring a HRTF typically involve generating a sound field at a given position by a test signal from the sound source S, which may include one or more transducers, and subsequently measuring a resultant sound field at a position of the listener by one or more other transducers, such as microphones (not shown in FIG. 1). In such methods, a test subject, either live or simulated, is located at one position, and microphones are placed in or near the ear canals of the test subject. The test subject is generally in a stationary position throughout the measurement process and movement of the test subject is discouraged.
Usually, the sound source is located at a position remote from the position of the test subject, for example, at a distance r and angles A and B in relation to the position of the test subject, and a test signal is produced by the sound source and measured by the transducers located at or near the ear canals of the test subject. The sound source is then typically moved to another position, for example, at a same distance r and angle A and a different angle B relative to the position of the test subject, and the process is repeated until HRTFs have been measured for each desired relative position of the sound source.
The accurate movement and positioning of the sound source is often time consuming. Therefore, multiple sound sources are often utilized and located at multiple positions, such that the time required for setup and measurement is minimized. In this case, the equipment needed to position the multiple sound sources has a typical drawback of being large and unwieldy and unsuitable for general commercial use.
There exists a need for an improved system, apparatus and method for measuring a HRTF quickly, accurately and with ease.